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c0c852dd18
Martin mentioned that the verifier cannot assume arguments from
LSM hook sk_alloc_security being trusted since after the hook
is called, the sk ref_count is set to 1. This will overwrite
the ref_count changed by the bpf program and may cause ref_count
underflow later on.
I then further checked some other hooks. For example,
for bpf_lsm_file_alloc() hook in fs/file_table.c,
f->f_cred = get_cred(cred);
error = security_file_alloc(f);
if (unlikely(error)) {
file_free_rcu(&f->f_rcuhead);
return ERR_PTR(error);
}
atomic_long_set(&f->f_count, 1);
The input parameter 'f' to security_file_alloc() cannot be trusted
as well.
Specifically, I investiaged bpf_map/bpf_prog/file/sk/task alloc/free
lsm hooks. Except bpf_map_alloc and task_alloc, arguments for all other
hooks should not be considered as trusted. This may not be a complete
list, but it covers common usage for sk and task.
Fixes: 3f00c52393 ("bpf: Allow trusted pointers to be passed to KF_TRUSTED_ARGS kfuncs")
Signed-off-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/r/20221203204954.2043348-1-yhs@fb.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
83 lines
1.7 KiB
C
83 lines
1.7 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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/*
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* Copyright (C) 2020 Google LLC.
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*/
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#ifndef _LINUX_BPF_LSM_H
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#define _LINUX_BPF_LSM_H
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#include <linux/sched.h>
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#include <linux/bpf.h>
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#include <linux/lsm_hooks.h>
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#ifdef CONFIG_BPF_LSM
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#define LSM_HOOK(RET, DEFAULT, NAME, ...) \
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RET bpf_lsm_##NAME(__VA_ARGS__);
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#include <linux/lsm_hook_defs.h>
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#undef LSM_HOOK
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struct bpf_storage_blob {
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struct bpf_local_storage __rcu *storage;
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};
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extern struct lsm_blob_sizes bpf_lsm_blob_sizes;
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int bpf_lsm_verify_prog(struct bpf_verifier_log *vlog,
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const struct bpf_prog *prog);
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bool bpf_lsm_is_sleepable_hook(u32 btf_id);
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bool bpf_lsm_is_trusted(const struct bpf_prog *prog);
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static inline struct bpf_storage_blob *bpf_inode(
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const struct inode *inode)
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{
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if (unlikely(!inode->i_security))
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return NULL;
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return inode->i_security + bpf_lsm_blob_sizes.lbs_inode;
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}
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extern const struct bpf_func_proto bpf_inode_storage_get_proto;
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extern const struct bpf_func_proto bpf_inode_storage_delete_proto;
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void bpf_inode_storage_free(struct inode *inode);
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void bpf_lsm_find_cgroup_shim(const struct bpf_prog *prog, bpf_func_t *bpf_func);
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#else /* !CONFIG_BPF_LSM */
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static inline bool bpf_lsm_is_sleepable_hook(u32 btf_id)
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{
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return false;
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}
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static inline bool bpf_lsm_is_trusted(const struct bpf_prog *prog)
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{
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return false;
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}
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static inline int bpf_lsm_verify_prog(struct bpf_verifier_log *vlog,
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const struct bpf_prog *prog)
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{
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return -EOPNOTSUPP;
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}
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static inline struct bpf_storage_blob *bpf_inode(
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const struct inode *inode)
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{
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return NULL;
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}
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static inline void bpf_inode_storage_free(struct inode *inode)
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{
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}
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static inline void bpf_lsm_find_cgroup_shim(const struct bpf_prog *prog,
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bpf_func_t *bpf_func)
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{
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}
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#endif /* CONFIG_BPF_LSM */
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#endif /* _LINUX_BPF_LSM_H */
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